I forgot to mention the measures are each scored as either 1 or 0 so I just need to know which n categories have the lowest combined scores.
Maybe you could create a seperate calculated field for each of the measures that flags the values in the top 5. Then you could add each of these calculated fields to either the filter pane or to the colour shelf.
Have I oversimplified the problem?
Are you able to post a sample workbook (twbx file)?
One option may be to add together all the measures. Then, do the top n from there.